Joash Ogwoka
Due to the dangers associate with heart surgery, it is important to understand the mechanisms underlying mitral valve prolapse(MVR) and mitral regurgitation(MR) in order to best determine the conditions under which surgical intervention may be necessary. MVP is defined as “single or bileaflet prolapse at least 2 mm beyond the long-axis annular plane”(Hayek) while MR is defined as a backflow of blood into the left atrium. Complications do not usually occur in MVPbut some may occur such as cardiac death.MR however, depending on the severity, acute or chronic, may cause may complication atrial fibrillation or heart failure.In MR, due to an opening in the mitral valve, true isovolumetric contraction is not possible. Blood flows into the left atrium once left ventricular pressure surpass that of the left atrium. Afterload/resistance is reduced and the end-systolic volume is decreased. These two facts account for the shift to the left observed in the PV-loop and accounts for the curved shape observed in at the LVESV. Likewise, true isovolumetric relaxation is not possible in MR. Blood continues to flow into the left atrium after aortic valve closure due to a still elevated left ventricular pressure relative to the left atrium. Consequently, increased atrial pressure and increased left ventricular compliance, shown to occur in MR, lead to an elevated LVEDV. These two facts lead to the curved shape shown on the PV-loop at LVEDV. It is also important to note that although, the stroke volume increases, the blood ejected is lower than that of the normal heart. The stroke volume in MR include the blood volume pumped back into the left atrium. Current understanding concerning when surgical intervention is necessary is limited. The presence of a simulator that mimic natural heart conditions and output may aid healthcare provider in making proper surgical recommendation. With a simulator, it is possible to input different condition for every patient and determine whether the value observed in the clinic are due to MVP/MR, in which case surgery would be productive, or other conditions that may not be aided by surgery. This distinction is necessary as heart surgery isdangerous. Therefore, by making the comparison of simulator value to those provided in literature, a step closer to isolating functional simulators is possible.
Materials
1. Software: Cardiosimulator by Antaki Lab
The EF value is known to decrease in patients afflicted with mitral insufficiency, or mitral regurgitation(MR). A decrease in EF values would simulate MR afflicted patients. Therefore, in order to simulate MR, the ejection fractions(EF) presented by Gaasch et al. of 65%, 55%, and 45% were translated into the cardiosimulator as 6.5, 5.5, and 4.5 under the slot labeled regurgitation - mitral valve. The above value for MVP simulation were preserved for the MR simulation. Since MR and MVP are related, the MR simulation was sufficient in simulation the presence of MR and MVP as coexisting conditions.
The Cardiosimulator showed no change between normal and mitral valve prolapse conditions. A slight shift from straight to curve-like in LVEDV was observed in the Cardiosimulator in the transition from a normal heart to MR heart but this was not deemed significant as this change was small and not repeatable over many simulations. The stroke volume, i.e. increase in LVEDV and decrease in LVESV, did not change from normal to MR heart. A slight decline in the stroke volume was observed in the simulator when transitioning from normal to MR heart conditions but again this was not deemed significant for the same reason outlined above. In all, an expected decrease in LVESV and increase in LVEDV, i.e. increase stroke volume, and shift from vertical to curved-like character in the isovolumetric contraction and true isovolumetric relaxation portions of the PV-loop was not observed.
1.https://www.cvphysiology.com/Heart%20Disease/HD009c 2. https://www.ahajournals.org/doi/epub/10.1161/CIRCULATIONAHA.107.755942